In the area of wireless communications, time division multiple access (TDMA) and code division multiple access (CDMA) protocols are used for communicating from a base station to a mobile station. The TDMA technology uses a single frequency for transmitting and receiving signals, while the CDMA systems use one frequency band for transmitting signals and another frequency band for receiving signals. In both cases, multipath can be a source of interference.
FIG. 1 is an example environment 100 in which multipath is typically present. The environment 100 includes a first antenna tower 105a and a second antenna tower 105b. Each antenna tower 105a, 105b has an associated base station (not shown). The environment 100 further includes a first office building 110a and a second office building 110b. In the first office building 110a, a subscriber unit 115 is within range of signals from both antenna towers 105a, 105b. 
There are several signaling paths from the antenna towers 105a, 105b to the subscriber unit 115. A first signaling path 120 is a direct signaling path from the first antenna tower 105a to the subscriber unit 115. A second signaling path 125 includes a reflection off the second office building 110b as the respective signal travels from the first antenna tower 105a to the subscriber unit 115. A third signaling path 130 is a direct signaling path from the second antenna tower 105b to the subscriber unit 115.
The first signaling path 120 is in the direction of the first antenna tower 105a. The subscriber unit 115 does not know where the first antenna tower 105a is located. The subscriber unit 115 can only point (i.e., direct a beam) in the direction of the strongest desired signal, if the subscriber signal is equipped with a steering antenna. The strongest desired signal is in the direction between the locations of the first antenna tower 105a and second office building 110b. 
In direction finding (DF), multipath tends to be harmful because it masks the true direction of the signal. The component of the multipath that is in-phase with the first signaling path 120 is actually helpful, and thus, the direction change is inconsequential. So, multipath is not all interference. However, the third signaling path 130 is all interference because it is not the same signal as being transmitted on the first signaling path and can never be in-phase with the signal on the first signaling path.
If the subscriber unit 115 employs a phased array antenna, it can use the phased array antenna to steer an associated antenna beam toward the first antenna tower 105a, or, in the case of multipath as just described, in the direction of the strongest desired signal. Additionally, the phased array antenna may be used to steer the associated antenna beam to receive signals from only the direct signaling path 120 from the first antenna tower 105a to remove the multipath effects (i.e., signal fading) caused by the second signal 125 or interference caused by the third signaling path 130.
FIG. 2 is a block diagram of the phased array antenna used by the subscriber unit 115 of FIG. 1 capable of steering the associated beam, where the steering is done by phase shifting the RF signals to/from the antenna elements composing the array antenna 200. The phased array antenna 200 is composed of antenna sub-assemblies 205. Each antenna sub-assembly 205 includes an antenna element 210, duplexer 215, and phase shifter 220. A control signal 225 is used to adjust the phase shifts imposed by each of the phase shifters 220.
In transmission mode, the sub-assemblies 205 of phased array antenna 200 receives a signal 230. The signal is phase shifted by the phase shifters 220 in a manner where, when the beams of all the antenna elements 210 are combined, the resulting effective beam (not shown) is directed as defined by the control signals 225. The signal 230 passes from the phase shifters 220 to the antenna elements 210 via the duplexes 215, which are in a transmit mode.
In receive mode, the antenna elements 210 receive RF signals most strongly from a direction defined by the same control signals 225. The antenna elements 210 provide the received signals to the duplexes 215, which are set in a receive mode to allow the received RF signal to pass to the phase shifters 220. The phase shifters 220 provide signals 230, which have been phase shifted, to a summer (not shown) to reconstruct the signal. The reconstructed signal is thereafter processed by a receiver (not shown).